In wireless communication systems, wireless service providers may operate radio access networks (RANs), each RAN including a number of base stations radiating to provide coverage in which to serve user equipment devices (UEs) such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped communication devices. In turn, each base station may be coupled with network infrastructure that provides connectivity with one or more transport networks, such as the public switched telephone network (PSTN) and/or the Internet for instance. With this arrangement, a UE within coverage of the RAN may engage in air interface communication with a base station and may thereby communicate via the base station with various remote network entities or with other UEs served by the base station.
Further, a RAN may operate in accordance with a particular air interface protocol, examples of which include, without limitation, Orthogonal Frequency Division Multiple Access (OFDMA (e.g., Long Term Evolution (LTE) and Wireless Interoperability for Microwave Access (WiMAX)), Code Division Multiple Access (CDMA) (e.g., 1×RTT and 1×EV-DO), Global System for Mobile Communications (GSM), IEEE 802.11 (WIFI), BLUETOOTH, and others. Each protocol may define its own procedures for registration of UEs, initiation of communications, handover between base station coverage areas, and other functions.
In order to utilize legacy cellular networks, a service provider may implement a hybrid wireless communication system that includes multiple separate but interconnected RANs. For example, a service provider may implement a first RAN that provides high speed data communications, and a second RAN that provides traditional telephony service, with each RAN providing air interface coverage according to a different air interface protocol. In such an arrangement, a UE may acquire connectivity with and be served by the first RAN and may at some point transition to instead connect with and be served by the second RAN. For instance, some existing hybrid systems include an LTE RAN (e.g., the LTE RAN discussed above) for data communications and a circuit-switched RAN, such as a CDMA RAN (or GSM RAN or the like), for legacy telephone service.
A UE that operates in a hybrid system may be configured as a single radio device, which utilizes the same radio system for communications on both networks in the hybrid system. In the context of a hybrid system utilizing LTE for data communications, a UE with the capability of using one radio system for both LTE communication and communication under at least one other protocol (e.g., CDMA) may be referred to as a single-radio LTE (SRLTE) device or an SRLTE UE. Similarly, when using a single radio system to engage in communication under LTE and at least one other protocol may be referred to as operating in an SRLTE mode.
When operating in a hybrid system, an SRLTE UE can register with both the LTE network and the CDMA network. However, when LTE service is available, an SRLTE UE will remain connected to the LTE network, except for cases when communication via the CDMA network is needed, such as tuning away to listen for pages or initiate a voice call via the CDMA network. As such, an SRLTE UE periodically disconnects from the LTE network and tunes to the CDMA network (e.g., at scheduled paging occasions) to check for any page messages directed to the UE from the CDMA network. If the SRLTE UE does not receive a page from the CDMA network, then UE, it will re-connect to the LTE network.
By way of example, in an LTE RAN, each base station (LTE evolved Node-B (eNodeB)) has a communication interface with a signaling controller known as a mobility management entity (MME), the base station and MME each also have a respective communication interface with a gateway system that provides connectivity with a packet-switched transport network, and the base station has a communication interface with each of its neighboring base stations.
In example operation, when a UE enters into coverage of an LTE base station on a particular carrier, the UE signals to the base station to initiate an attach process and to establish a radio-link-layer connection with the base station. In this process, the base station signals to the MME, the MME authenticates the UE, the MME and base station obtain and store a context/profile record for the UE, and the gateway system assigns an IP address to the UE for use by the UE to communicate on the packet-switched transport network. Further, at this point or later, the MME may engage in signaling with the base station and the gateway system to establish for the UE one or more bearers for carrying packet data between the UE and the transport network.
A CDMA RAN may include one or more base transceiver stations (BTSs) (e.g., macro network cell towers and/or femtocells), each of which may radiate to define a cell and cell sectors in which UEs can operate. Further, the RAN may include one or more base station controllers (BSCs) (which may also be referred to as radio network controllers (RNCs)) or the like, which may be integrated with or otherwise in communication with the BTSs, and which may include or be in communication with a switch or gateway that provides connectivity with one or more transport networks. Conveniently with this arrangement, a cell phone, personal digital assistant, wirelessly equipped computer, or other UE that is positioned within coverage of the RAN can then communicate with a BTS and in turn, via the BTS, with other served devices or with other entities on the transport network.
According to illustrative CDMA protocols, the forward link may define (i) a pilot channel on which the RAN may broadcast a pilot signal to allow UEs to detect wireless coverage, (ii) system parameter channels (e.g., a sync channel) on which the RAN may broadcast system operational parameters for reference by UEs so that the UEs can then seek network access, (iii) paging channels on which the RAN may broadcast page messages to alert UEs of incoming communications, and (iv) traffic channels on which the RAN may transmit bearer traffic (e.g., application data) for receipt by UEs. And the reverse link, for example, may define (i) access channels on which UEs may transmit “access probes” such as registration messages and call origination requests, and (ii) traffic channels on which UEs may transmit bearer traffic for receipt by the RAN.
When a UE seeks to initiate a voice call via a CDMA network, the UE may request that network resources be allocated for the voice call. As part of this process, the RAN determines the transmit power to use for forward-link traffic. To do so, the RAN may first transmit at an initial transmit power, which is typically a constant power level that is preset at the RAN. The UE then evaluates the forward-link signal quality, such as by determining the frame error rate (FER), and reports back to the RAN. Then, depending on the signal quality, the RAN may increase or decrease the transmit power by a predetermined increment. The RAN and UE may then repeat this process until a satisfactory signal quality is achieved.
Further, for certain types of communication, such as voice calls, video calls, and/or other types of calls, a UE may be able to use two or more different types of codecs when engaging in such communication. Each codec may have different characteristics that impact the extent of resources used when the UEs are communicating.